Re: [PATCH v3 1/9] dt-bindings: iio: adc: support the TI ADS126x ADC family

On 8/9/26 3:26 AM, Kurt Borja wrote:
> On Sat Aug 8, 2026 at 1:38 PM -05, David Lechner wrote:
>> On 8/7/26 10:58 PM, Kurt Borja wrote:
>>> The ADS1262 and ADS1263 are 32-bit, 38.4-kSPS delta-sigma ADCs with an
>>> integrated PGA, internal reference, excitation and burn-out current
>>> sources for sensor biasing and diagnostics. The ADS1263 adds a second,
>>> 24-bit delta-sigma ADC (ADC2) for background measurements.
>>>
>>
>> ...
>>
>>> +patternProperties:
>>> +  "^ain([0-9]|com)-supply$":
>>> +    description:
>>> +      Common-mode voltage supply connected to AIN<N> or AINCOM.
>>> +
>>> +  "^refp[1-3]-supply$":
>>> +    description:
>>> +      Positive voltage reference connected to REFP1 (AIN0), REFP2 (AIN2) or
>>> +      REFP3 (AIN4). If not described, its assumed to be connected to ground
>>> +      (0V).
>>
>> Would we really have a case with a negative only reference? I would say if not
>> described, assume the pin is free for other use.
> 
> In bipolar supply configurations, I believe it would make sense to wire
> the negative reference to -2.5V and ground the positive. Also we have
> the ti,reference-reversal case, where you may wire the "negative"
> reference to say 2.5V and the positive to ground.
> 

OK. I guess the better wording for both of these would be that if any
channel references one of these in reference-sources and it is not present
assume it is connected to ground (0V).

>>
>>> +
>>> +  "^refn[1-3]-supply$":
>>> +    description:
>>> +      Negative voltage reference connected to REFN1 (AIN1), REFN2 (AIN3) or
>>> +      REFN3 (AIN5). If not described, its assumed to be connected to ground
>>> +      (0V).
>>
>> Assumption is only true when corresponding refp supply is described. Otherwise
>> we should assume the pin is free for other uses.
> 
> I'll clarify it.
> 
>>
>>> +
>>> +  "^ti,refp[1-3]-refn[1-3]-resistor-ohms$":
>>> +    description:
>>> +      Magnitude of the external reference resistor connected between REFP<N>
>>> +      and REFN<M>. In ratiometric configurations, such as RTD measurements, the
>>> +      IDAC excitation current returns through this resistor, generating the
>>> +      reference voltage for the conversion.
>>> +
>>> +  "^channel@[0-9]+$":
>>> +    $ref: /schemas/iio/adc/adc.yaml#
>>> +    unevaluatedProperties: false
>>> +
>>> +    properties:
>>> +      reg:
>>> +        maxItems: 1
>>> +
>>> +      single-channel:
>>> +        minimum: 0
>>> +        maximum: 10
>>> +
>>> +      common-mode-channel:
>>> +        minimum: 0
>>> +        maximum: 10
>>> +        default: 10
>>> +
>>> +      diff-channels:
>>> +        description: |
>>> +          In addition to the analog input pins 0 (AIN0) - 10 (AINCOM), there are
>>> +          special inputs that can be selected from the following values:
>>> +          11: Temperature sensor monitor
>>> +          12: Analog power supply monitor
>>> +          13: Digital power supply monitor
>>> +          14: TDAC test signal
>>
>> For reasons mentioned in the reply to the cover letter, I'm not a fan of the
>> monitor channels here.
>>
>>> +        items:
>>> +          minimum: 0
>>> +          maximum: 14
>>> +
>>
>> ...
>>
>>> +      input-chopping: true
>>> +
>>> +      ti,idac-rotation:
>>
>> Should we make this one a standard property like input-chopping?
> 
> Maybe excitation-current-chopping or excitation-channel-chopping?

I suppose. All of the TI literature seems to call it "rotation" rather
than "chopping", but I did find a few other sources that call it
"chopping" and that would be consistent with input-chopping.

I would go with excitation-channel-chopping since we are swapping
the current generators, not just the current magnitude.

> 
>>
>>> +        $ref: /schemas/types.yaml#/definitions/flag
>>> +        description:
>>> +          Automatically swap the IDAC1 and IDAC2 connections of alternate
>>> +          conversions. The ADC averages the alternate conversions to eliminate
>>> +          IDAC mismatch.
>>> +
>>
>> ...
>>
>>> +examples:
>>> +  - |
>>> +    #include <dt-bindings/gpio/gpio.h>
>>> +    #include <dt-bindings/interrupt-controller/irq.h>
>>> +
>>> +    spi {
>>> +        #address-cells = <1>;
>>> +        #size-cells = <0>;
>>> +
>>> +        adc@0 {
>>> +            compatible = "ti,ads1262";
>>> +            reg = <0>;
>>> +            spi-max-frequency = <8000000>;
>>> +            spi-cpha;
>>> +            avdd-supply = <&avdd>;
>>> +            dvdd-supply = <&dvdd>;
>>> +            #address-cells = <1>;
>>> +            #size-cells = <0>;
>>> +
>>> +            interrupts-extended = <&gpio 0 IRQ_TYPE_EDGE_FALLING>;
>>> +            interrupt-names = "drdy";
>>> +
>>> +            /* Typical common mode voltage configuration */
>>> +            aincom-supply = <&ads1262_vbias>;
>>> +
>>> +            regulators {
>>> +                ads1262_vbias: vbias {
>>> +                    regulator-name = "vbias";
>>
>> The node name is already "vbias" so giving regulator-name is redundant.
> 
> Is it okay to leave it empty?
> 
>     ads1262_vbias: vbias { };
> 

Yes. (Unless make dt_binding_check says otherwise.)

>>
>>> +                };
>>> +            };
>>> +
>>> +            channel@0 {
>>> +                reg = <0>;
>>> +                single-channel = <0>;
>>> +                /* The VBIAS is enabled on pin 10 (AINCOM) */
>>> +                common-mode-channel = <10>;
>>> +            };
>>> +        };
>>> +    };
>>> +
>